Vacation in Vanuatu - a few questions

I'm planning a trip for my gilfriend and I and Vanuatu seems like the most ideallic and beautiful place ever and I'm dead keen on taking her there. We're also both into our scuba diving and this seems right up our alley.
I have a few questions though:
Do we need to stay in the capital of Port Vila as I'm a bit wary of capital cities with regards to development and pollution, etc. We're wanting a really unspoilt and picturesque destination so would it be better for me to stay on an island such as Santo? And if We opt to do this, is it fairly easy to get around?
I hear there are some really good dives in Santo, are there any other islands I should look into including in my itinerary?

Any suggestions and advice will be greatly appreciated.
Many thanks in advance